Triangle Baffle?

[southpaw17er]

How would the diffraction look for a driver mounted in a triangular baffle?

Assuming a sphere is the best for diffraction, the end of a cylinder (or a 2D circle) the worst, and a rectangle somewhere in the middle, where does the triangle fit (both equilateral and acute or obtuse)??

I can't seem to find this mentioned anywhere...

Thanks in advance.

Ted

 

[Vikash]

The cylinder is worst assuming the driver is mounted in the centre because all edges of the baffle are equidistant from the driver edge. Mount if off-centre and the story changes.

So you can see that a triangle baffle has potential if you can spread out the driver to baffle edge distances.

Search for a program by one of our members called 'the edge' IIRC. You should be able to simulate this for yourself

 

[Vikash]

here it is: http://www.tolvan.com/edge/

 

[southpaw17er]

Thanks for the info Vikash, very useful program.

But what about a spiral baffle, in which the center of the driver is a different distance to all parts of the edge of the baffle (as seen in my artistic attachment).

Any ideas, since I can't simulate this in the program.

 

[Variac]

It depends on how you are using the baffle.
Are you hanging it in the air? Set on top of a bass box?
On the floor?

I have considered the same issues. I am using a rectangular one now which actually has quite a few different distances, so really isn't bad.

Lets think of a variety of possibilities.

 

[poptart]

I'm a newbie, but I've been wondering about the same thing, open baffle shapes. It seems the spiral, or a mirrored one like a cardioid would do the job, but would it be noticeably better than a rectangle to make it worth the added work?

I guess I don't understand why these peaks and valleys happen, I think it has something to do with the distance from the speaker to to the baffle edge being an even multiple of the wavelength of certain frequencies, but I can't clearly picture what's happening. If anyone could explain with the basic case of a speaker in the center of a round baffle it would really help me out

I also wonder why the baffle is always flat, what happens if you give it some thickness? If you move from the speaker in the center of a flat baffle case to a speaker in the "hole" of a donut, what changes? (please don't say everything )

 

[Vikash]

Thanks for the info Vikash, very useful program.

But what about a spiral baffle, in which the center of the driver is a different distance to all parts of the edge of the baffle (as seen in my artistic attachment).

Any ideas, since I can't simulate this in the program.

I made the observation many moons ago:
Here's an animation that attempts to illustrate the concept of baffle edge diffraction for various baffle shapes.

It requires a SVG Plugin plugin (if it's not already installed in IE).

As mentioned, any close room boundaries can extend the baffle.

 

[Vikash]

I'm a newbie, but I've been wondering about the same thing, open baffle shapes. It seems the spiral, or a mirrored one like a cardioid would do the job, but would it be noticeably better than a rectangle to make it worth the added work?

I guess I don't understand why these peaks and valleys happen, I think it has something to do with the distance from the speaker to to the baffle edge being an even multiple of the wavelength of certain frequencies, but I can't clearly picture what's happening. If anyone could explain with the basic case of a speaker in the center of a round baffle it would really help me out

I also wonder why the baffle is always flat, what happens if you give it some thickness? If you move from the speaker in the center of a flat baffle case to a speaker in the "hole" of a donut, what changes? (please don't say everything )

I'm no expert but I'll give it a shot.
Of all the baffle shapes usually described, the sphere is the only one considered on all three axis. The point here being that the front wave has a more gradual slope in merging with the rear wave as the edge of the baffle is reached thus producing a smoother baffle step transition.

The other shapes are concerned with having different lengths from driver edge to baffle edge (although the fall off is sudden) to again try and smooth out the half-space to full-space transition. This is why rounding over baffle edges (on a bog standard rectangular baffle) is a good idea, although it is requires a large radius for any real effect, and also mounting drivers off centre.

But how many big commercial rectangular baffle designs do this...

 

[Vikash]

A good starting point: http://www.t-linespeakers.org/tech/bafflestep/intro-bds.html

 

[poptart]

Thanks, that explains what's happening in the low frequencies well. I guess this thread isn't about open baffle speakers, so my question about what causes the peaks and dips in the higher frequencies isn't in the right place here.

 

[SY]

There's a great explanation in Beranek's "Acoustics." It's a book anyone interested in speakers (and audio in general) should have.

Basically, it's an interference effect caused when the sound waves hit the discontinuity where the baffle ends and are diffracted. The diffracted waves will have interference with the direct wave causing cancellation and reinforcement at different frequencies (depending on the timing between diffracted and direct wave).

 

[poptart]

I don't have that book, but I found some explanations online and thought I should post links for all the other beginner's out there like me:

http://www.speakerdesign.net/understand.html
http://www.linkwitzlab.com/diffraction.htm
http://www.linkwitzlab.com/faq.htm#Q8

It seems there's some debate about how audible the ripples in the frequency response above the bass slope are? Somewhat analogous to early reflections off a wall, you get a delayed version of the signal mixing with the direct sound.

 

[soongsc]

Thanks for the info Vikash, very useful program.

But what about a spiral baffle, in which the center of the driver is a different distance to all parts of the edge of the baffle (as seen in my artistic attachment).

Any ideas, since I can't simulate this in the program.

You can get an approximattion by selecting more corners in the EDGE and pulling the corners into that kind of shape.

 

[Variac]

A cardiod will have 2 equal paths because its symetrical. So the snail design is good. But what happens in the part where it suddenly jumps back to a smaller size? Maybe thats the places where it sits on a bass box or on the floor !

Rounding the edges or curving the baffle should be helpful. Some claim rounding doesn't help until the radius is about 3"

This subject should apply to open baffles or closed boxes. One reason that open baffles don't curve too much is that you are then starting to add sides which could creatwe the beginnings of a box, and the reflections you are trying to avoid with the OB.

 

[kneadle]

This topic intrigued me so much that I stopped using baffles altogether.

Dave

 

[poptart]

This topic intrigued me so much that I stopped using baffles altogether.

care to elaborate?

A cardiod will have 2 equal paths because its symmetrical

True, but every given distance will have those two paths, so no single distance would be emphasized would it? It seems equivalent to me, but what do I know? not much!

In my mind there's also a little voice that keeps saying "those longer parts are bound to be multiples of the shorter ones" so some frequencies are going to find more than one path that's a multiple of it's wavelength anyhow right? Would a rectangle with the same size shortest and and longest paths as the snail be pretty similar?

 

[kneadle]

care to elaborate?

Sure...I remember studying this at length, trying to come up for a solution with triangle shaped baffles. I couldn't really settle on a satisfactory solution, so I thought: why not figure out a way to mount a speaker on a baffle-less enclosure?

Oila. The Caterpillars.
http://www.t-linespeakers.org/projects/davidduke/index.html

I don't have any baffle refractions to deal with in this design. I think this would be called "cutting the Gordian knot."

Dave

 

[Variac]

Maybe the refractions are all at the edge of the driver and equidistint- maybe you really haven't eliminated them,,,,

 

[Audiophilenoob]

Maybe the refractions are all at the edge of the driver and equidistint- maybe you really haven't eliminated them,,,,

can you ever truly "eliminate" them?

 

[Variac]

I don't think so......